Length-based indicators of fishery and ecosystem status: Glover's Reef Marine Reserve, Belize

Abstract

For the spear gun fishery at Glover's Reef, Belize, we used catch length frequencies to infer whether each of the eight most common species was likely to be overfished (spawning stock biomass<target) or experiencing overfishing (fishing mortality rate F>natural mortality rate M). We used Monte Carlo simulations to determine whether the results were sensitive to uncertainty about natural mortality, asymptotic length, growth rate and length at maturity. We found that black grouper Mycteroperca bonaci is overfished, and Nassau grouper Epinephelus striatus, schoolmaster snapper Lutjanus apodus and mutton snapper Lutjanus analis are probably overfished, but hogfish Lachnolaimus maximus, stoplight parrotfish Sparisoma viride, French angelfish Pomacanthus paru and gray angelfish Pomacanthus arcuatus are probably not overfished. All species except French angelfish were experiencing overfishing across a range of life history parameters. Nassau grouper, black grouper and mutton snapper were often caught below the size at maturity Lm. The results were sensitive to different assumed values of the life history parameters. Life history parameters can vary regionally for many reef fishes, and there have been few life history studies in the western Caribbean; such studies would greatly improve estimates of stock status. We also calculated six multispecies indicators of fishery status. The mean length relative to Lm was greater than 1.0 and constant between 2005 and 2011. Mean trophic level, mean maximum size, and fraction piscivores increased between 2005 and 2011, partly due to the fact that parrotfish, previously an important component of the catch, have been prohibited beginning in 2009. Mean catch per unit effort declined. Given that black grouper, Nassau grouper, mutton snapper and schoolmaster snapper are found to be overfished and experiencing overfishing under most values of the life history parameters, we recommend size or catch limits for these species.